Parameter estimation for determining hydraulic properties of a fine sand from transient flow measurements

A cone penetrometer method for measuring hydraulic conductivity of unsaturated soils at depth is under development. Successful advancement of this method hinges on using parameter estimation to obtain hydraulic parameter values from pore water pressure and flow rate data. A finite element model is employed to predict flow responses, and objective functions describe differences between ''true'' and simulated responses. Contour plots in parameter space show the relative sensitivity of objective functions to field-saturated hydraulic conductivity, K-fs, field-saturated moisture content, theta(fs), and the van Genuchten hydraulic parameters, alpha and n. Principal curvatures and directions in parameter space describe the nature of objective functions near ''true'' parameter values. An objective function based on flow rate and pore water pressures does not provide better parameter sensitivity than one based on pore water pressures alone. It appears possible to obtain estimates of K-fs and alpha but unlikely that the other parameters will be identifiable.